Coated abrasive disc and methods of making and using the same

ABSTRACT

A coated abrasive disc includes a disc backing having an outer circumference. An abrasive layer is disposed on the disc backing. The abrasive layer comprises triangular abrasive platelets secured to a major surface of the disc backing by at least one binder material. The triangular abrasive platelets are disposed at least 70 percent of regularly-spaced points along an arithmetic spiral pattern extending outwardly toward the outer circumference. Each one of the triangular abrasive platelets has respective top and bottom surfaces connected to each other, and separated by, three sidewalls. On a respective basis, one sidewall of at least 90 percent of each of the triangular abrasive platelets disposed facing and proximate to the disc backing, and is lengthwise aligned within 10 degrees of being tangent to the arithmetic spiral pattern. Methods of making and using the coated abrasive disc are also disclosed.

TECHNICAL FIELD

The present disclosure broadly relates to coated abrasive discs, methodsof making them, and methods of using them.

BACKGROUND

Coated abrasive discs made from triangular abrasive platelets are usefulfor abrading, finishing, or grinding a wide variety of materials andsurfaces in the manufacturing of goods. In particular, high-pressureoff-hand grinding of carbon steel by off-hand abrading with a handheldright-angle grinder is an important application for coated abrasivediscs. In view of the above, there continues to be a need for improvingthe cost, performance, and/or life of the coated abrasive discs.

Coated abrasive articles having rotationally aligned triangular abrasiveplatelets are disclosed in U.S. Pat. No. 9,776,302 (Keipert). The coatedabrasive articles have a plurality of triangular abrasive platelets eachhaving a surface feature. The plurality of triangular abrasive plateletsis attached to a flexible backing by a make coat comprising a resinousadhesive forming an abrasive layer. The surface features have aspecified Z-axis rotational orientation that occurs more frequently inthe abrasive layer than would occur by a random Z-axis rotationalorientation of the surface feature.

SUMMARY

In one aspect, the present disclosure provides a coated abrasive disccomprising:

a disc backing having an outer circumference;

an abrasive layer disposed on the disc backing, wherein the abrasivelayer comprises triangular abrasive platelets secured to a major surfaceof the disc backing by at least one binder material, wherein thetriangular abrasive platelets are disposed at least 70 percent ofregularly-spaced points along an arithmetic spiral pattern extendingoutwardly toward the outer circumference,

wherein each one of the triangular abrasive platelets has respective topand bottom surfaces connected to each other, and separated by, threesidewalls, and

wherein, on a respective basis, one sidewall of at least 90 percent ofeach of the triangular abrasive platelets disposed facing and proximateto the disc backing, and is lengthwise aligned within 10 degrees ofbeing tangent to the arithmetic spiral pattern.

Advantageously, coated abrasive discs according to the presentdisclosure are useful for high-pressure off-hand abrading of carbonsteel, where they exhibit superior performance as compared to previoussimilar discs.

Accordingly, in a second aspect, the present disclosure provides amethod of abrading a workpiece, the method comprising frictionallycontacting a portion of the abrasive layer of a coated abrasive discaccording to the present disclosure with a workpiece, and moving atleast one of the workpiece and the coated abrasive disc relative to theother to abrade the workpiece.

In a third aspect, the present disclosure provides a method of making acoated abrasive disc, the method comprising:

disposing a curable make layer precursor on a major surface of a discbacking;

adhering triangular abrasive platelets into the curable make layerprecursor, wherein the triangular abrasive platelets are disposed atleast 70 percent of regularly-spaced points along an arithmetic spiralpattern extending outwardly toward the outer circumference,

wherein the triangular abrasive platelets comprise triangular abrasiveplatelets, wherein each one of the triangular abrasive platelets hasrespective top and bottom surfaces connected to each other, andseparated, by three sidewalls, and

wherein, on a respective basis, one sidewall of at least 90 percent ofeach of the triangular abrasive platelets is entirely disposed proximatethe disc backing, and is lengthwise aligned within 10 degrees of beingtangent to the arithmetic spiral pattern;

at least partially curing the curable make layer precursor to provide amake layer, disposing a curable size layer precursor over the make layerand triangular abrasive platelets; and

at least partially curing the curable size layer precursor to provide asize layer.

As used herein:

The term “mild steel” refers to a carbon-based steel alloy containingless than about 0.25 percent by weight of carbon.

The term “offhand abrading” means abrading where the operator manuallyurges the disc/wheel against a workpiece or vice versa.

The term “proximate” means very near or next to (e.g., contacting orembedded in a binder layer contacting).

The term “spiral” refers to a spiral which is planar. In some preferredembodiments, the spiral may be an arithmetic spiral, also known as an“Archimedean spiral”. An arithmetic spiral has the property that any rayfrom the origin intersects successive turnings of the spiral in pointswith a constant separation distance.

The term “workpiece” refers to a thing being abraded.

As used herein, the term “triangular abrasive platelet”, means a ceramicabrasive particle with at least a portion of the abrasive particlehaving a predetermined shape that is replicated from a mold cavity usedto form the shaped precursor abrasive particle. Except in the case ofabrasive shards (e.g., as described in U.S. Pat. Appl. Publ.2009/0169816 A1 (Erickson et al.) the triangular abrasive platelet willgenerally have a predetermined geometric shape that substantiallyreplicates the mold cavity that was used to form the triangular abrasiveplatelet. Triangular abrasive platelet as used herein excludes randomlysized abrasive particles obtained by a mechanical crushing operation.

As used herein, “Z-axis rotational orientation” refers to the angularrotation, about a Z-axis perpendicular to the major surface of the discbacking, of the longitudinal dimension the triangular abrasive plateletsidewall that most faces the disc backing.

Features and advantages of the present disclosure will be furtherunderstood upon consideration of the detailed description as well as theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic top view of exemplary coated abrasive disc 100.

FIG. 1A is an enlarged view of region 1A in FIG. 1.

FIG. 1B is an enlarged view of region 1B in FIG. 1A.

FIG. 1C is a schematic cross-sectional view of coated abrasive disc 100taken along line 1C-1C in FIG. 1B.

FIG. 2A is a schematic top view of exemplary triangular abrasiveplatelet 130 a.

FIG. 2B is a schematic perspective view of exemplary triangular abrasiveplatelet 130 a.

FIG. 3A is a schematic top view of exemplary triangular abrasiveplatelet 330 b.

FIG. 3B is a schematic side view of exemplary triangular abrasiveplatelet 330 b.

FIG. 4 is a schematic top view of a production tool 400 useful formaking coated abrasive disc 100.

FIG. 4A is an enlarged view of region 4A in FIG. 4.

FIG. 4B is an enlarged view of region 4B in FIG. 4A.

FIG. 4C is an enlarged schematic cross-sectional view of production tool400 taken along line 4C-4C in FIG. 4B illustrating cavity 420.

FIG. 4D is an enlarged schematic cross-sectional view of production tool400 taken along line 4D-4D in FIG. 4B illustrating cavity 420.

Repeated use of reference characters in the specification and drawingsis intended to represent the same or analogous features or elements ofthe disclosure. It should be understood that numerous othermodifications and embodiments can be devised by those skilled in theart, which fall within the scope and spirit of the principles of thedisclosure. The figures may not be drawn to scale.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary coated abrasive disc 100 according to thepresent disclosure, wherein triangular abrasive platelets 130 aresecured at precise locations and Z-axis orientations to a disc backing110.

Referring now to FIGS. 1 and 1A-1C, abrasive layer 120 disposed on amajor surface 115 of disc backing 110. Abrasive layer 120 comprisestriangular abrasive platelets 130 secured to major surface 115 of discbacking 110 by at least one binder material (shown as make layer 132 andsize layer 134). Optional supersize layer 156 overlays size layer 134.Triangular abrasive platelets 130 are disposed at regularly-spacedpoints 138 along an arithmetic spiral pattern 140 extending outwardlytoward outer circumference 142. On a respective basis, one sidewall ofat least 90 percent of each of the triangular abrasive platelets 130disposed facing and proximate to the disc backing is lengthwise alignedwithin 10 degrees of being tangent to the arithmetic spiral pattern 140at the corresponding points 138. In this regard, collinear and parallelconfigurations are to be considered as being aligned at zero degreesrelative to the tangent.

The disc backing may comprise any known coated abrasive backing, forexample. In some embodiments, the disc backing comprises a continuousuninterrupted disc, while in others it may have a central arbor hole formounting. Likewise, the disc backing may be flat or it may have adepressed central hub, for example, a Type 27 depressed center disc. Thedisc backing may be rigid, semi-rigid, or flexible. In some embodiments,the backing has a mechanical fastener, or adhesive fastener securelyattached to a major surface opposite the abrasive layer. Suitablematerials for the substrate include polymeric films, metal foils, wovenfabrics, knitted fabrics, paper, vulcanized fiber, nonwovens, foams,screens, laminates, combinations thereof, and treated versions thereof.For off-hand grinding applications where stiffness and cost areconcerns, vulcanized fiber backings are typically preferred. Forapplications where stiffness of the backing is desired, a flexiblebacking may also be used by affixing it to a rigid backup pad mounted tothe grinding tool.

The disc backing is generally circular and preferably rotationallysymmetric around its center. Preferably it has a circular perimeter, butit may have additional features along the perimeter such as, forexample, in the case of a scalloped perimeter.

The abrasive layer may comprise a single binder layer having abrasiveparticles retained therein, or more typically, a multilayer constructionhaving make and size layers. Coated abrasive discs according to thepresent disclosure may include additional layers such as, for example,an optional supersize layer that is superimposed on the abrasive layer,or a backing antistatic treatment layer may also be included, ifdesired. Exemplary suitable binders can be prepared from thermallycurable resins, radiation-curable resins, and combinations thereof.

The make layer can be formed by coating a curable make layer precursoronto a major surface of the backing. The make layer precursor maycomprise, for example, glue, phenolic resin, aminoplast resin,urea-formaldehyde resin, melamine-formaldehyde resin, urethane resin,free-radically polymerizable polyfunctional (meth)acrylate (e.g.,aminoplast resin having pendant α,β-unsaturated groups, acrylatedurethane, acrylated epoxy, acrylated isocyanurate), epoxy resin(including bis-maleimide and fluorene-modified epoxy resins),isocyanurate resin, and mixtures thereof. Of these, phenolic resins arepreferred, especially when used in combination with a vulcanized fiberbacking.

Phenolic resins are generally formed by condensation of phenol andformaldehyde, and are usually categorized as resole or novolac phenolicresins. Novolac phenolic resins are acid-catalyzed and have a molarratio of formaldehyde to phenol of less than 1:1. Resole (also resol)phenolic resins can be catalyzed by alkaline catalysts, and the molarratio of formaldehyde to phenol is greater than or equal to one,typically between 1.0 and 3.0, thus presenting pendant methylol groups.Alkaline catalysts suitable for catalyzing the reaction between aldehydeand phenolic components of resole phenolic resins include sodiumhydroxide, barium hydroxide, potassium hydroxide, calcium hydroxide,organic amines, and sodium carbonate, all as solutions of the catalystdissolved in water.

Resole phenolic resins are typically coated as a solution with waterand/or organic solvent (e.g., alcohol). Typically, the solution includesabout 70 percent to about 85 percent solids by weight, although otherconcentrations may be used. If the solids content is very low, then moreenergy is required to remove the water and/or solvent. If the solidscontent is very high, then the viscosity of the resulting phenolic resinis too high which typically leads to processing problems.

Phenolic resins are well-known and readily available from commercialsources. Examples of commercially available resole phenolic resinsuseful in practice of the present disclosure include those marketed byDurez Corporation wider the trade designation VARCUM (e.g., 29217,29306, 29318, 29338, 29353); those marketed by Ashland Chemical Co. ofBartow, Fla. under the trade designation AEROFENE (e.g., AEROFENE 295);and those marketed by Kangnam Chemical Company Ltd. of Seoul, SouthKorea under the trade designation PHENOLITE (e.g., PHENOLITE TD-2207).

The make layer precursor may be applied by any known coating method forapplying a make layer to a backing such as, for example, including rollcoating, extrusion die coating, curtain coating, knife coating, gravurecoating, and spray coating.

The basis weight of the make layer utilized may depend, for example, onthe intended use(s), type(s) of abrasive particles, and nature of thecoated abrasive disc being prepared, but typically will be in the rangeof from 1, 2, 5, 10, or 15 grams per square meter (gsm) to 20, 25, 100,200, 300, 400, or even 600 gsm. The make layer may be applied by anyknown coating method for applying a make layer (e.g., a make coat) to abacking, including, for example, roll coating, extrusion die coating,curtain coating, knife coating, gravure coating, and spray coating.

Once the make layer precursor is coated on the backing, the triangularabrasive platelets are applied to and embedded in the make layerprecursor. The triangular abrasive platelets are applied nominallyaccording to a predetermined pattern and Z-axis rotational orientationonto the make layer precursor.

Triangular abrasive platelets are disposed at regularly-spaced (i.e.,spaced apart at a constant interval) points along the arithmetic spiralpattern extending outwardly toward the outer circumference. At least 70percent (e.g., at least 80 percent or at least 90 percent or even atleast 95 percent) of the points 138 have one of the triangular abrasiveplatelets disposed thereat. The arithmetic spiral pattern may cover aportion of the major surface of the disc backing or the entire backing.

Referring now to FIGS. 2A and 2B, each one of triangular abrasiveplatelets 130 has respective top and bottom surfaces (162,164) connectedto each other, and separated, by three sidewalls 166 a, 166 b, 166 c.

One sidewall 166 a of at least 90 percent (e.g., at least 95 percent, atleast 99 percent, or even 100 percent) of the triangular abrasiveplatelets 130 is disposed facing (and preferably proximate to) discbacking 110 (see FIG. 1C). Further, each sidewall 166 that is disposedfacing disc backing 110 has a horizontal Z-axis 141 rotationalorientation e that is within 10 degrees (preferably within 5 degrees,and more preferably within 2 degrees) of the tangent 139 to thearithmetic spiral pattern at the respective point 138 where it isdisposed.

FIGS. 3A and 3B show another embodiment of a useful triangular abrasiveplatelets 330, triangular abrasive platelet 330 has respective top andbottom surfaces (332, 334) connected to each other, and separated by,three sloping sidewalls (336).

In this regard, the horizontal Z-axis rotational direction is consideredto be within 10 degrees of the tangent at a point on the spiral patternif its Z-axis projection onto the arithmetic spiral pattern 140 (whichis planar) intersects the tangent line at an angle of 10 degrees orless. Collinear and parallel configurations are considered to intersectthe tangent line at an angle of 0 degrees.

In some preferred embodiments, the spacing between the respective pointson the arithmetic spiral pattern is from 1 to 3 times, more preferably1.2 to 2 times, and even more preferably 1.2 to 1.7 times the averagelength of the sidewalls of the triangular abrasive platelets that arefacing the fiber disc backing, although other spacings may also be used.

It is permissible that some of the regularly-spaced points along thearithmetic spiral may not have a triangular abrasive platelet disposedat that location. In preferred embodiments, at least 70 percent(preferably at least 80 percent, more preferably at least 90 percent,and more preferably at least 95 percent) of contiguous regularly-spacedpoints adjacent to points occupied by a triangular abrasive plateletalso have a triangular abrasive platelet disposed thereat.

In some embodiments, the triangular abrasive platelets are shaped asthin triangular prisms, while in other embodiments, the triangularabrasive platelets are shaped as truncated triangular pyramids(preferably with a taper angle of about 8 degrees). The triangularabrasive platelets may have different side lengths, but are preferablyequilateral on their largest face.

The triangular abrasive platelets have sufficient hardness to functionas abrasive particles in abrading processes. Preferably, the triangularabrasive platelets have a Mohs hardness of at least 4, at least 5, atleast 6, at least 7, or even at least 8. Preferably, they comprise alphaalumina.

Crushed abrasive or non-abrasive particles may be included in theabrasive layer between the abrasive elements and/or abrasive platelets,preferably in sufficient quantity to form a closed coat (i.e.,substantially the maximum possible number of particles of nominalspecified grade(s) that can be retained in the abrasive layer).

Examples of suitable abrasive particles include: fused aluminum oxide;heat-treated aluminum oxide; white fused aluminum oxide; ceramicaluminum oxide materials such as those commercially available under thetrade designation 3M CERAMIC ABRASIVE GRAIN from 3M Company. St. Paul,Minn.; brown aluminum oxide; blue aluminum oxide; silicon carbide(including green silicon carbide); titanium diboride; boron carbide;tungsten carbide; garnet; titanium carbide; diamond; cubic boronnitride; garnet; fused alumina zirconia; iron oxide; chromia; zirconia;titania; tin oxide; quartz; feldspar flint; emery; sol-gel-derivedabrasive particles; and combinations thereof. Of these, molded sol-gelderived alpha alumina triangular abrasive platelets are preferred inmany embodiments. Abrasive material that cannot be processed by asol-gel route may be molded with a temporary or permanent binder to formshaped precursor particles which are then sintered to form triangularabrasive platelets, for example, as described in U.S. Pat. Appln. Publ.No. 2016/0068729 A1 (Erickson et al.).

Examples of sol-gel-derived abrasive particles and methods for theirpreparation can be found in U.S. Pat. No. 4,314,827 (Leitheiser et al.);U.S. Pat. No. 4,623,364 (Cottringer et al.): U.S. Pat. No. 4,744,802(Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.); and U.S. Pat. No.4,881,951 (Monroe et al.). It is also contemplated that the abrasiveparticles could comprise abrasive agglomerates such, for example, asthose described in U.S. Pat. No. 4,652,275 (Bloecher et al.) or U.S.Pat. No. 4,799,939 (Bloecher et al.). In some embodiments, thetriangular abrasive platelets may be surface-treated with a couplingagent (e.g., an organosilane coupling agent) or other physical treatment(e.g., iron oxide or titanium oxide) to enhance adhesion of the abrasiveparticles to the binder (e.g., make and/or size layer). The abrasiveparticles may be treated before combining them with the correspondingbinder precursor, or they may be surface treated in situ by including acoupling agent to the binder.

Preferably, the triangular abrasive platelets comprise ceramic abrasiveparticles such as, for example, sol-gel-derived polycrystalline alphaalumina particles. Triangular abrasive platelets composed ofcrystallites of alpha alumina, magnesium alumina spinel, and a rareearth hexagonal aluminate may be prepared using sol-gel precursor alphaalumina particles according to methods described in, for example, U.S.Pat. No. 5,213,591 (Celikkaya et al.) and U.S. Pat. Appn. Publ. Nos.2009/0165394 A1 (Culler et al.) and 2009/0169816 A1 (Erickson et al.).

Alpha alumina-based triangular abrasive platelets can be made accordingto well-known multistep processes. Briefly, the method comprises thesteps of making either a seeded or non-seeded sol-gel alpha aluminaprecursor dispersion that can be converted into alpha alumina; fillingone or more mold cavities having the desired outer shape of thetriangular abrasive platelet with the sol-gel, drying the sol-gel toform precursor triangular abrasive platelets; removing the precursortriangular abrasive platelets from the mold cavities; calcining theprecursor triangular abrasive platelets to form calcined, precursortriangular abrasive platelets, and then sintering the calcined,precursor triangular abrasive platelets to form triangular abrasiveplatelets. The process will now be described in greater detail.

Further details concerning methods of making sol-gel-derived abrasiveparticles can be found in, for example, U.S. Pat. No. 4,314,827(Leitheiser); U.S. Pat. No. 5,152,917 (Pieper et al.); U.S. Pat. No.5,435,816 (Spurgeon et al.); U.S. Pat. No. 5,672,097 (Hoopman et al.);U.S. Pat. No. 5,946,991 (Hoopman et al.); U.S. Pat. No. 5,975,987(Hoopman et al.); and U.S. Pat. No. 6,129,540 (Hoopman et al.); and inU.S. Publ. Pat. Appln. No. 2009/0165394 A1 (Culler et al.).

The triangular abrasive platelets may include a single kind oftriangular abrasive platelets or a blend of two or more sizes and/orcompositions of triangular abrasive platelets. In some preferredembodiments, the triangular abrasive platelets are precisely-shaped inthat individual triangular abrasive platelets will have a shape that isessentially the shape of the portion of the cavity of a mold orproduction tool in which the particle precursor was dried, prior tooptional calcining and sintering.

Triangular abrasive platelets used in the present disclosure cantypically be made using tools (i.e., molds) cut using precisionmachining, which provides higher feature definition than otherfabrication alternatives such as, for example, stamping or punching.Typically, the cavities in the tool surface have planar faces that meetalong sharp edges, and form the sides and top of a truncated pyramid.The resultant triangular abrasive platelets have a respective nominalaverage shape that corresponds to the shape of cavities (e.g., truncatedpyramid) in the tool surface however, variations (e.g., randomvariations) from the nominal average shape may occur during manufacture,and triangular abrasive platelets exhibiting such variations areincluded within the definition of triangular abrasive platelets as usedherein.

In some embodiments, the base and the top of the triangular abrasiveplatelets are substantially parallel, resulting in prismatic ortruncated pyramidal shapes, although this is not a requirement. In someembodiments, the sides of a truncated trigonal pyramid have equaldimensions and form dihedral angles with the base of about 82 degrees.However, it will be recognized that other dihedral angles (including 90degrees) may also be used. For example, the dihedral angle between thebase and each of the sides may independently range from 45 to 90degrees, typically 70 to 90 degrees, more typically 75 to 85 degrees.

As used herein in referring to triangular abrasive platelets, the term“length” refers to the maximum dimension of a triangular abrasiveplatelet. “Width” refers to the maximum dimension of the triangularabrasive platelet that is perpendicular to the length. The terms“thickness” or “height” refer to the dimension of the triangularabrasive platelet that is perpendicular to the length and width.

Examples of sol-gel-derived triangular alpha alumina (i.e., ceramic)abrasive particles can be found in U.S. Pat. No. 5,201,916 (Berg); U.S.Pat. No. 5,366,523 (Rowenhorst (Re 35,570)); and U.S. Pat. No. 5,984,988(Berg). Details concerning such abrasive particles and methods for theirpreparation can be found, for example, in U.S. Pat. No. 8,142,531(Adefris et al.); U.S. Pat. No. 8,142,891 (Culler et al.); and U.S. Pat.No. 8,142,532 (Erickson et al.); and in U.S. Pat. Appl. Publ. Nos.2012/0227333 (Adefris et al.); 2013/0040537 (Schwabel et al.); and2013/0125477 (Adefris).

The triangular abrasive platelets are typically selected to have alength in a range of from 1 micron to 15000 microns, more typically 10microns to about 10000 microns, and still more typically from 150 to2600 microns, although other lengths may also be used.

Triangular abrasive platelets are typically selected to have a width ina range of from 0.1 micron to 3500 microns, more typically 100 micronsto 3000 microns, and more typically 100 microns to 2600 microns,although other lengths may also be used.

Triangular abrasive platelets are typically selected to have a thicknessin a range of from 0.1 micron to 1600 microns, more typically from 1micron to 1200 microns, although other thicknesses may be used.

In some embodiments, triangular abrasive platelets may have an aspectratio (length to thickness) of at least 2, 3, 4, 5, 6, or more.

Surface coatings on the triangular abrasive platelets may be used toimprove the adhesion between the triangular abrasive platelets and abinder in coated abrasive discs, or can be used to aid in electrostaticdeposition of the triangular abrasive platelets. In one embodiment,surface coatings as described in U.S. Pat. No. 5,352,254 (Celikkaya) inan amount of 0.1 to 2 percent surface coating to triangular abrasiveplatelet weight may be used. Such surface coatings are described in U.S.Pat. No. 5,213,591 (Celikkaya et al.); U.S. Pat. No. 5,011,508 (Wald etal.); U.S. Pat. No. 1,910,444 (Nicholson); U.S. Pat. No. 3,041,156(Rowse et al.); U.S. Pat. No. 5,009,675 (Kunz et al.); U.S. Pat. No.5,085,671 (Martin et al.); U.S. Pat. No. 4,997,461 (Markhoff-Matheny etal.); and U.S. Pat. No. 5,042,991 (Kunz et al.). Additionally, thesurface coating may prevent the triangular abrasive platelet fromcapping. Capping is the term to describe the phenomenon where metalparticles from the workpiece being abraded become welded to the tops ofthe triangular abrasive platelets. Surface coatings to perform the abovefunctions are known to those of skill in the art.

The abrasive particles may be independently sized according to anabrasives industry recognized specified nominal grade. Exemplaryabrasive industry recognized grading standards include those promulgatedby ANSI (American National Standards Institute), FEPA (Federation ofEuropean Producers of Abrasives), and JIS (Japanese IndustrialStandard). ANSI grade designations (i.e., specified nominal grades)include, for example: ANSI 4, ANSI 6, ANSI 8, ANSI 16, ANSI 24, ANSI 36,ANSI 46, ANSI 54, ANSI 60, ANSI 70, ANSI 80, ANSI 90, ANSI 100, ANSI120, ANSI 150, ANSI 180, ANSI 220, ANSI 240, ANSI 280, ANSI 320, ANSI360, ANSI 400, and ANSI 600, FEPA grade designations include F4, F5, F6,F7, F8, F10, F12, F14, F16, F16, F20, F22, F24, F30, F36, F40, F46, F54,F60, F70, F80, F90, F100, F120, F150, F180, F220, F230, F240, F280,F320, F360, F400, F500, F600, F800, F1000, F1200, F1500, and F2000. JISgrade designations include JIS8, JIS12, JIS16, JIS24, JIS36, JIS46,JIS54, JIS60, JIS80, JIS100, JIS150, JIS180, JS220, JIS240, JIS280,JS320, JS360, JS400, JIS600, JIS800, JIS1000, JIS1500, JIS2500, JIS4000,JIS6000, JIS8000, and JIS10000. According to one embodiment of thepresent disclosure, the average diameter of the abrasive particles maybe within a range of from 260 to 1400 microns in accordance with FEPAgrades F60 to F24.

Alternatively, the abrasive particles can be graded to a nominalscreened grade using U.S.A. Standard Test Sieves conforming to ASTM E-11“Standard Specification for Wire Cloth and Sieves for Testing Purposes”.ASTM E-11 prescribes the requirements for the design and construction oftesting sieves using a medium of woven wire cloth mounted in a frame forthe classification of materials according to a designated particle size.A typical designation may be represented as −18+20 meaning that theabrasive particles pass through a test sieve meeting ASTM E-11specifications for the number 18 sieve and are retained on a test sievemeeting ASTM E-11 specifications for the number 20 sieve. In oneembodiment, the abrasive particles have a particle size such that mostof the particles pass through an 18 mesh test sieve and can be retainedon a 20, 25, 30, 35, 40, 45, or 50 mesh test sieve. In variousembodiments, the abrasive particles can have a nominal screened gradeof: −18+20, −20/+25, −25+30, −30+35, −35+40, 5−40+45, −45+50, −50+60,−60+70, −70/+80, −80+100, −100+120, −120+140, −140+170, −170+200,−200+230, −230+270, −270+325, −325+400, −400+450, −450+500, or −500+635.Alternatively, a custom mesh size can be used such as −90+100.

The arithmetic spiral pattern can be characterized by its pitch (i.e.,the regular separation between lines of the spiral pattern whiletraveling radially outward from the real or theoretical center of thespiral pattern. In some preferred embodiments, the arithmetic spiralpattern pitch is from 1.2 to 3 times, more preferably 1.2 to 2.5 times,and even more preferably 1.2 to 2 times the thickness of the triangularabrasive platelets, although this is not a requirement. Likewise, insome preferred embodiments, the regularly-spaced interval is from 1 to 3times, more preferably from 1.2 to 2 times, and even more preferably 1.2to 1.5 times the length of the triangular abrasive platelets, althoughthis is not a requirement.

Coated abrasive discs according to the present disclosure can be made bya method in which the triangular abrasive platelets are precisely placedand oriented. The method generally involves the steps of filling thecavities in a production tool each with one or more triangular abrasiveplatelets (typically one or two), aligning the filled production tooland a make layer precursor-coated backing for transfer of the triangularabrasive platelets to the make layer precursor, transferring theabrasive particles from the cavities onto the make layerprecursor-coated backing, and removing the production tool from thealigned position. Thereafter, the make layer precursor is at leastpartially cured (typically to a sufficient degree that the triangularabrasive platelets are securely adhered to the backing), a size layerprecursor is then applied over the make layer precursor and abrasiveparticles, and at least partially cured to provide the coated abrasivedisc. The process, which may be batch or continuous, can be practiced byhand or automated, e.g., using robotic equipment. It is not required toperform all steps or perform them in consecutive order, but they can beperformed in the order listed or additional steps performed in between.

The triangular abrasive platelets can be placed in a desired rotationalorientation (e.g., Z-axis rotational orientation) by first placing themin appropriately shaped cavities in a dispensing surface of a productiontool arranged to have a complementary arithmetic spiral pattern.

An exemplary production tool 400 for making the coated abrasive disc 100shown in FIGS. 1 and 1A-1C, formed by casting a thermoplastic sheet 415,is shown in FIGS. 4 and 4A-4D. Referring now to FIGS. 4 and 4A-4D,production tool 400 has a dispensing surface 410 comprising anarithmetic spiral pattern 430 of cavities 420 sized and shaped toreceive the triangular abrasive platelets. Cavities 420 are Z-axisrotationally aligned so that when filled with triangular abrasiveplatelets that when they are subsequently transferred they form thedesired corresponding arithmetic spiral pattern and Z-axis rotationalorientation in the resultant coated abrasive disc.

Once most, or all, of the cavities are filled with the desired number oftriangular abrasive platelets the dispensing surface is brought intoclose proximity or contact with the make layer precursor layer on thedisc backing thereby adhering (e.g., embedding and/or contacting) andtransferring the triangular abrasive platelets from the production toolto the make layer precursor while nominally maintaining horizontalorientation. Of course, some unintended loss of orientation may occur,but it should generally be manageable within the ±10 degrees or lesstolerance.

In some embodiments, the depth of the cavities in the production tool isselected such that the triangular abrasive platelets fit entirely withinthe cavities. In some preferred embodiments, the triangular abrasiveplatelets extend slightly beyond the openings of the cavities. In thisway, they can be transferred to the make layer precursor by directcontact with reduced chance of resin transfer to the to the productiontool. In some preferred embodiments, the center of mass for eachtriangular abrasive platelet resides within a respective cavity of theproduction tool when the triangular abrasive platelet is fully insertedinto the cavity. If the depth of the cavities becomes too short, withthe triangular abrasive platelet's center of mass being located outsideof the cavity, the triangular abrasive platelets are not readilyretained within the cavities and may jump back out as the productiontool is used in the apparatus.

In order to fill the cavities in the production tool, an excess of thetriangular abrasive platelets is preferably applied to the dispensingsurface of the production tool such that more triangular abrasiveplatelets are provided than the number of cavities. An excess oftriangular abrasive platelets, which means that there are moretriangular abrasive platelets present per unit length of the productiontool than cavities present, helps to ensure that most cavities withinthe production tool are eventually filled with a triangular abrasiveplatelet as the triangular abrasive platelets accumulate onto thedispensing surface and are moved about either due to gravity or othermechanically applied forces to translate them into a cavity. Since thebearing area and spacing of the abrasive particles is often designedinto the production tooling for the specific grinding application, it isgenerally desirable to not have too much variability in the number ofunfilled cavities.

Preferably, a majority of the cavities in the dispensing surface arefilled with a triangular abrasive platelet disposed in an individualcavity such that the sides of the cavity and platelet are at leastapproximately parallel. This can be accomplished by shaping the cavitiesslightly larger than the triangular abrasive platelets (or multiplethereof). To facilitate filling and release it may be desirable that thecavities have inwardly sloping sidewalls with increasing depth and/orhave vacuum openings at the bottoms of the cavities, wherein the vacuumopening lead to a vacuum source. It is desirable to transfer thetriangular abrasive platelets onto the make layer precursor-coatedbacking such that they stand up or are erectly applied. Therefore, thecavity shape is designed to hold the triangular abrasive plateleterectly.

In various embodiments, at least 60, 70, 80, 90, or 95 percent of thecavities in the dispensing surface contain a triangular abrasiveplatelet. In some embodiments, gravity can be used to fill the cavities.In other embodiments, the production tool can be inverted and vacuumapplied to hold the triangular abrasive platelets in the cavities. Thetriangular abrasive platelets can be applied by spray, fluidized bed(air or vibration), or electrostatic coating, for example. Removal ofexcess triangular abrasive platelets would be done by gravity as anyabrasive particles not retained would fall back down. The triangularabrasive platelets can thereafter be transferred to the make layerprecursor-coated disc backing by removing vacuum.

As mentioned above, excess triangular abrasive platelets may be suppliedthan cavities such that some will remain on the dispensing surface afterthe desired number of cavities have been filled. These excess triangularabrasive platelets can often be blown, wiped, or otherwise removed fromthe dispensing surface. For example, a vacuum or other force could beapplied to hold the triangular abrasive platelets in the cavities andthe dispensing surface inverted to clear it of the remaining fraction ofthe excess triangular abrasive platelets.

In preferred embodiments, the production tool is formed of athermoplastic polymer such as, for example, polyethylene, polypropylene,polyester, or polycarbonate from a metal master tool. Fabricationmethods of production tools, and of master tooling used in theirmanufacture, can be found in, for example, U.S. Pat. No. 5,152,917(Pieper et al.); U.S. Pat. No. 5,435,816 (Spurgeon et al.); U.S. Pat.No. 5,672,097 (Hoopman et al.); U.S. Pat. No. 5,946,991 (Hoopman etal.); U.S. Pat. No. 5,975,987 (Hoopman et al.); and U.S. Pat. No.6,129,540 (Hoopman et al.); and U.S. Pat. Appl. Publ. No. 2013/0344786A1 (Keipert) and 2016/0311084 A1 (Culler et al.).

In preferred embodiments, the production tool is produced by additivemanufacturing or “3-D printing”, of a suitable thermoplastic, thermosetor radiation curable resin.

Once the triangular abrasive platelets have been embedded in the makelayer precursor, it is at least partially cured in order to preserveorientation of the mineral during application of the size layerprecursor. Typically, this involves B-staging the make layer precursor,but more advanced cures may also be used if desired. B-staging may beaccomplished, for example, using heat and/or light and/or use of acurative, depending on the nature of the make layer precursor selected.

Next, the size layer precursor is applied over the at least partiallycured make layer precursor and triangular abrasive platelets. The sizelayer can be formed by coating a curable size layer precursor onto amajor surface of the backing. The size layer precursor may comprise, forexample, glue, phenolic resin, aminoplast resin, urea-formaldehyderesin, melamine-formaldehyde resin, urethane resin, free-radicallypolymerizable polyfunctional (meth)acrylate (e.g., aminoplast resinhaving pendant α,β-unsaturated groups, acrylated urethane, acrylatedepoxy, acrylated isocyanurate), epoxy resin (including bis-maleimide andfluorene-modified epoxy resins), isocyanurate resin, and mixturesthereof. If phenolic resin is used to form the make layer, it islikewise preferably used to form the size layer. The size layerprecursor may be applied by any known coating method for applying a sizelayer to a backing, including roll coating, extrusion die coating,curtain coating, knife coating, gravure coating, spray coating, and thelike. If desired, a presize layer precursor or make layer precursoraccording to the present disclosure may be also used as the size layerprecursor.

The basis weight of the size layer will also necessarily vary dependingon the intended use(s), type(s) of abrasive particles, and nature of thecoated abrasive disc being prepared, but generally will be in the rangeof from 1 or 5 gsm to 300, 400, or even 500 gsm, or more. The size layerprecursor may be applied by any known coating method for applying a sizelayer precursor (e.g., a size coat) to a backing including, for example,roll coating, extrusion die coating, curtain coating, and spray coating.

Once applied, the size layer precursor, and typically the partiallycured make layer precursor, are sufficiently cured to provide a usablecoated abrasive disc. In general, this curing step involves thermalenergy, although other forms of energy such as, for example, radiationcuring may also be used. Useful forms of thermal energy include, forexample, heat and infrared radiation. Exemplary sources of thermalenergy include ovens (e.g., festoon ovens), heated rolls, hot airblowers, infrared lamps, and combinations thereof.

In addition to other components, binder precursors, if present, in themake layer precursor and/or presize layer precursor of coated abrasivediscs according to the present disclosure may optionally containcatalysts (e.g., thermally activated catalysts orphotocatalysts),free-radical initiators (e.g., thermal initiators or photoinitiators),curing agents to facilitate cure. Such catalysts (e.g., thermallyactivated catalysts or photocatalysts), free-radical initiators (e.g.,thermal initiators or photoinitiators), and/or curing agents may be ofany type known for use in coated abrasive discs including, for example,those described herein.

In addition to other components, the make and size layer precursors mayfurther contain optional additives, for example, to modify performanceand/or appearance. Exemplary additives include grinding aids, fillers,plasticizers, wetting agents, surfactants, pigments, coupling agents,fibers, lubricants, thixotropic materials, antistatic agents, suspendingagents, and/or dyes.

Exemplary grinding aids, which may be organic or inorganic, includewaxes, halogenated organic compounds such as chlorinated waxes liketetrachloronaphthalene, pentachloronaphthalene, and polyvinyl chloride;halide salts such as sodium chloride, potassium cryolite, sodiumcryolite, ammonium cryolite, potassium tetrafluoroborate, sodiumtetrafluoroborate, silicon fluorides, potassium chloride, magnesiumchloride; and metals and their alloys such as tin, lead, bismuth,cobalt, antimony, cadmium, iron, and titanium. Examples of othergrinding aids include sulfur, organic sulfur compounds, graphite, andmetallic sulfides. A combination of different grinding aids can be used.

Exemplary antistatic agents include electrically conductive materialsuch as vanadium pentoxide (e.g., dispersed in a sulfonated polyester),humectants, carbon black and/or graphite in a binder.

Examples of useful fillers for this disclosure include silica such asquartz, glass beads, glass bubbles and glass fibers; silicates such astalc, clays. (montmorillonite) feldspar, mica, calcium silicate, calciummetasilicate, sodium aluminosilicate, sodium silicate; metal sulfatessuch as calcium sulfate, barium sulfate, sodium sulfate, aluminum sodiumsulfate, aluminum sulfate; gypsum; vermiculite; wood flour, aluminumtrihydrate; carbon black; aluminum oxide; titanium dioxide; cryolite;chiolite; and metal sulfites such as calcium sulfite.

Optionally a supersize layer may be applied to at least a portion of thesize layer. If present, the supersize typically includes grinding aidsand/or anti-loading materials. The optional supersize layer may serve toprevent or reduce the accumulation of swarf (the material abraded from aworkpiece) between abrasive particles, which can dramatically reduce thecutting ability of the coated abrasive disc. Useful supersize layerstypically include a grinding aid (e.g., potassium tetrafluoroborate),metal salts of fatty acids (e.g., zinc stearate or calcium stearate),salts of phosphate esters (e.g., potassium behenyl phosphate), phosphateesters, urea-formaldehyde resins, mineral oils, crosslinked silanes,crosslinked silicones, and/or fluorochemicals. Useful supersizematerials are further described, for example, in U.S. Pat. No. 5,556,437(Lee et al.). Typically, the amount of grinding aid incorporated intocoated abrasive products is about 50 to about 400 gsm, more typicallyabout 80 to about 300 gsm. The supersize may contain a binder such asfor example, those used to prepare the size or make layer, but it neednot have any binder.

Further details concerning coated abrasive discs comprising an abrasivelayer secured to a backing, wherein the abrasive layer comprisesabrasive particles and make, size, and optional supersize layers arewell known, and may be found, for example, in U.S. Pat. No. 4,734,104(Broberg); U.S. Pat. No. 4,737,163 (Larkey); U.S. Pat. No. 5,203,884(Buchanan et al.); U.S. Pat. No. 5,152,917 (Pieper et al.); U.S. Pat.No. 5,378,251 (Culler et al.); U.S. Pat. No. 5,417,726 (Stout et al.);U.S. Pat. No. 5,436,063 (Follett et al.); U.S. Pat. No. 5,496,386(Broberg et al.); U.S. Pat. No. 5,609,706 (Benedict et al.); U.S. Pat.No. 5,520,711 (Helnin); U.S. Pat. No. 5,954,844 (Law et al.); U.S. Pat.No. 5,961,674 (Gagliardi et al.); U.S. Pat. No. 4,751,138 (Bange etal.); U.S. Pat. No. 5,766,277 (DeVoe et al.); U.S. Pat. No. 6,077,601(DeVoe et al.); U.S. Pat. No. 6,228,133 (Thurber et al.); and U.S. Pat.No. 5,975,988 (Christianson).

Coated abrasive discs according to the present disclosure are useful forabrading a workpiece; for example, by off-hand abrading with a handheldright-angle grinder. Preferred workpieces include welding beads (e.g.,especially mild steel welds), flash, gates, and risers off castings.

Select Embodiments of the Present Disclosure

In a first aspect, the present disclosure provides a coated abrasivedisc comprising:

a disc backing having an outer circumference;

an abrasive layer disposed on the disc backing, wherein the abrasivelayer comprises triangular abrasive platelets secured to a major surfaceof the disc backing by at least one binder material, wherein thetriangular abrasive platelets are disposed at least 70 percent(preferably at least 80 percent, more preferably at least 90 percent) ofregularly-spaced points along an arithmetic spiral pattern extendingoutwardly toward the outer circumference,

wherein each one of the triangular abrasive platelets has respective topand bottom surfaces connected to each other, and separated by, threesidewalls, and

wherein, on a respective basis, one sidewall of at least 90 percent ofeach of the triangular abrasive platelets disposed facing and proximateto the disc backing, and is lengthwise aligned within 10 degrees ofbeing tangent to the arithmetic spiral pattern.

In a second embodiment, the present disclosure provides a coatedabrasive disc according to the first embodiment, wherein the triangularabrasive platelets have an average thickness, and wherein the arithmeticspiral pattern has a pitch that is 1.2 to 3 times the average thicknessof the triangular abrasive platelets.

In a third embodiment, the present disclosure provides a coated abrasivedisc according to the first or second embodiment, wherein the abrasivelayer further comprises crushed abrasive or non-abrasive particles.

In a fourth embodiment, the present disclosure provides a coatedabrasive disc according to any one of the first to third embodiments,wherein the disc backing comprises vulcanized fiber.

In a fifth embodiment, the present disclosure provides a coated abrasivedisc according to any one of the first to fourth embodiments, whereinthe abrasive layer comprises a make layer and a size layer disposed overthe make layer and the triangular abrasive platelets.

In a sixth embodiment, the present disclosure provides a coated abrasivedisc according to any one of the first to fifth embodiments, wherein thetriangular abrasive platelets comprise alpha alumina.

In a seventh embodiment, the present disclosure provides a method ofabrading a workpiece, the method comprising frictionally contacting aportion of the abrasive layer of a coated abrasive disc according to anyone of the first to sixth embodiments with the workpiece, and moving atleast one of the workpiece and the coated abrasive disc relative to theother to abrade the workpiece.

In an eighth embodiment, the present disclosure provides a method ofabrading a workpiece according to the seventh embodiment, wherein thesubstrate comprises a mild steel weld, and wherein the abrasive layercontacts the mild steel weld.

In a ninth embodiment, the present disclosure provides a method ofmaking a coated abrasive disc, the method comprising:

disposing a curable make layer precursor on a major surface of a discbacking;

adhering triangular abrasive platelets into the curable make layerprecursor, wherein the triangular abrasive platelets are disposed atleast 70 percent (preferably at least 80 percent, more preferably atleast 90 percent) of regularly-spaced points along an arithmetic spiralpattern extending outwardly toward the outer circumference,

wherein the triangular abrasive platelets comprise triangular abrasiveplatelets, wherein each one of the triangular abrasive platelets hasrespective top and bottom surfaces connected to each other, andseparated by, three sidewalls, and

wherein, on a respective basis, one sidewall of at least 90 percent ofeach of the triangular abrasive platelets disposed facing and proximateto the disc backing, and is lengthwise aligned within 10 degrees ofbeing tangent to the arithmetic spiral pattern;

at least partially curing the curable make layer precursor to provide amake layer, disposing a curable size layer precursor over the make layerand triangular abrasive platelets; and

at least partially curing the curable size layer precursor to provide asize layer.

In a tenth embodiment, the present disclosure provides a methodaccording to the ninth embodiment, wherein the triangular abrasiveplatelets have an average thickness, and wherein the arithmetic spiralpattern has a pitch that is 1.2 to 3 times the average thickness of thetriangular abrasive platelets.

In an eleventh embodiment, the present disclosure provides a methodaccording to the ninth or tenth embodiment, wherein the abrasive layerfurther comprises crushed abrasive or non-abrasive particles.

In a twelfth embodiment, the present disclosure provides a methodaccording to any one of the ninth to eleventh embodiments, wherein thedisc backing comprises vulcanized fiber.

In a thirteenth embodiment, the present disclosure provides a methodaccording to any one of the ninth to twelfth embodiments, wherein thetriangular abrasive platelets comprise alpha alumina.

Objects and advantages of this disclosure are further illustrated by thefollowing non-limiting examples, but the particular materials andamounts thereof recited in these examples, as well as other conditionsand details, should not be construed to unduly limit this disclosure.

EXAMPLES

Unless otherwise noted, all parts, percentages, ratios, etc. in theExamples and the rest of the specification are by weight. Unlessotherwise noted, all reagents were obtained, or are available fromchemical vendors such as, for example. Sigma-Aldrich Company, St. Louis.Mo., or may be synthesized by known methods. Abrasive particles used inthe Examples are reported in Table 1, below.

TABLE 1 ABBREVIATION DESCRIPTION AP1 Shaped abrasive particles wereprepared according to the disclosure of U.S. Pat. No. 8,142,531 (Adefriset al.). The shaped abrasive particles were prepared by molding aluminasol gel in equilateral triangle-shaped polypropylene mold cavities ofside length 0.11 inch (2.794 mm) and a mold depth of 0.028 inch (0.711mm). After drying and firing, the resulting shaped abrasive particleswere about 1.4 mm (side length) × 0.35 mm thick, with a draft angleapproximately 98 degrees, and would pass through a 20-mesh USA StandardTesting Sieve. AP2 Natural Almandite garnet conforming the ANSI standardfor grade 50, obtained under the trade designation 50UT from BartonAbrasives, Glen Falls, New York.

Example 1

A 7-inch (178-mm) circular plastic transfer tool consisting of an arrayof triangular cavities, having geometries such as those described in PCTPat. Publ. No. WO 2015/100018 A1 (Adefris et al.), was prepared by 3-Dprinting. The transfer tool pattern was a continuous spiral from centerto edge where all of the cavity openings were oriented substantiallyedgewise with respect to the grinding direction of the rotating coatedabrasive disc as shown in FIGS. 4 and 4A-4D. The cavity spacing down thelength of the spiral was approximately 9 per inch (3.5 per centimeter)and the spiral pitch was approximately 30 rows per inch (11.8 rows percentimeter). The total number of cavities on the disc was approximately10000. The transfer tool was treated with a molybdenum sulfide spraylubricant (obtained under the trade designation MOLYCOAT from the DowCorning Corporation. Midland, Mich.) to assist abrasive grain release.

An excess of abrasive grain AP1 was applied to the surface of thetransfer tool having the cavity openings and the tooling was shaken fromside to side by hand. The transfer tooling cavities were soon filledwith AP1 grains held in a vertex down and base up orientation andaligned along the cavity long axis. Additional AP1 was applied and theprocess repeated until greater than 95 percent of the transfer toolingcavities were filled by AP1 grain. Excess grain was removed from thesurface of the transfer tool leaving only the grains contained withinthe cavities.

A make resin was prepared by mixing 49 parts resole phenolic resin(based-catalyzed condensate from 1.5:1 to 2.1:1 molar ratio offormaldehyde:phenol), 41 parts of calcium carbonate (HUBERCARB, HuberEngineered Materials, Quincy, Ill.) and 10 parts of water, 2.8 grams ofmake resin was applied via a brush to a 7-inch (17.8-cm) diameter×0.83mm thick vulcanized fiber web (DYNOS VULCANIZED FIBER, DYNOS GmbH,Troisdorf. Germany) having a 0.875-inch (2.22-cm) center hole.

The AP1 filled transfer tool was placed cavity side up on a 7-inch by7-inch (18-cm×18-cm) square wooden board. The make resin coated surfaceof the vulcanized fiber disc was brought into contact with the filledtransfer tool and another 7-inch by 7-inch (18-cm×18-cm) square woodenboard was placed on top. The resulting assembly was inverted while beingheld in rigid contact and gently tapped to dislodge the AP1 grains fromthe transfer tool so as to fall base first onto the make resin surface.The vulcanized fiber disc backing was then allowed to fall away from thenow substantially grain-free transfer tool resulting in an AP1 coatedvulcanized fiber disc replicating the transfer tooling pattern.

A drop-coated filler grain consisting of AP2 was applied in excess tothe wet make resin and agitated until the entire exposed make resinsurface was filled to capacity with AP2. The disc was inverted to removeexcess AP2. The amount of AP2 addition was 16.0+/−0.5 grams.

The make resin was partially cured in an oven by heating for 45 minutesat 70° C., followed by 45 minutes at 90° C. followed by 3 hours at 105°C. The disc was then coated with 14.5+/−0.2 grams of a conventionalcryolite-containing phenolic size resin and cured for 45 minutes at 70°C., followed by 45 minutes at 90° C., followed by 16 hours at 105° C.EXAMPLE 1 was used to grind AISI 1020 steel tube using Grinding TestMethod A. Grinding performance results are reported in Table 2.

Example 2

EXAMPLE 2 was prepared as described in EXAMPLE 1. The amount of AP2 dropcoated secondary grain was 11+/−0.1 grams and the amount of cryolitesize resin was 13.7+/−0.1 grams. EXAMPLE 2 was used to grind AISI 1018mild steel using Grinding Test Method B. AISI 1018 mild steel has thecomposition, on a weight basis: 0.18 percent carbon, 0.6-0.9 percentmanganese, 0.04 percent (max) phosphorus, 0.05 percent (max) of sulfur,and 98.81-99.26 percent iron. Grinding performance results are reportedin Table 2.

Comparative Example A

COMPARATIVE EXAMPLE A was a commercially available electro-coatedvulcanized fiber disc (obtained under the trade designation 982C grade36+, 3M Company. Saint Paul, Minn.). COMPARATIVE EXAMPLE A was used togrind AISI 1018 mild steel using Grinding Test Method B. Grindingperformance results are reported in Table 2.

Comparative Example B

COMPARATIVE EXAMPLE B was prepared as described in EXAMPLE 1 with theexception as follows: The transfer tool cavities were arranged in arectangular array pattern as described in Example 4 in U.S. Pat. No.9,776,302 (Keipert). The cavity array was 17 per inch (6.7 percentimeter) in both horizontal and vertical directions for a totalcavity density of 289 per square inch (44.8 per square centimeter) orapproximately 10950 cavities for the entire tool. The transfer tool wasfilled with AP1 grain. The make resin amount was 3.0+/−0.1 grams. Thedrop coated secondary grain was 15.3+/−0.2 grams of AP2. The cryolitesize resin level was 14.6+/−0.1 grams. COMPARATIVE EXAMPLE B was used togrind AISI 1020 steel tube using Grinding Test Method A. Grindingperformance results are reported in Table 2.

Comparative Example C

COMPARATIVE EXAMPLE C was prepared as described in COMPARATIVE EXAMPLEB.

The transfer tool was filled with AP1 grain. The make resin amount was3.5 grams. The drop coated secondary grain was 9.4 grams of AP2. Thecryolite size resin level was 12.1 grams. COMPARATIVE EXAMPLE C was usedto grind 1018 mild steel using Grinding Test Method B. Grindingperformance results are reported in Table 2.

Grinding Test Method A

The grinding performance of the various discs was evaluated by grinding1020 mild carbon steel tubes using the following procedure. Seven-inch(17.8-cm) diameter coated abrasive discs for evaluation were attached toa drive motor running at a constant rotational speed of 6000 rpm andfitted with a 7-inch (17.8 cm) ribbed disc pad face plate (obtained as051144 EXTRA HARD RED RIBBED from 3M Company, St. Paul, Minn.). Thegrinder was activated and urged against an end face of a 1 inch (2.54cm) diameter, 0.125 inch (3.175 mm) wall thickness pre-weighed 1020steel tube under a controlled force of 20 pounds. The workpiece wasabraded under these conditions for 3.2-second grinding intervals(passes). Following each 3.2-second interval, the workpiece was cooledto room temperature and weighed to determine the cut of the abrasiveoperation. The test end point was determined when the cut fell below 12grams per cycle. Test results were reported as the incremental cut(g/cycle) for each interval and the total stock removed (g).

Method B

The grinding performance of the various discs was evaluated by grinding1018 mild carbon steel bars using the following procedure. Seven-inch(17.8-cm) diameter coated abrasive discs for evaluation were attached toa drive motor running at a constant rotational speed of 5000 rpm andfitted with a 7-inch (17.8 cm) ribbed disc pad face plate (obtained as051144 EXTRA HARD RED RIBBED from 3M Company, St. Paul, Minn.). Thegrinder was activated and urged against an end face of a 1×1 in(2.54×2.54 cm) pre-weighed 1018 steel bar under a controlled force. Theworkpiece was abraded under these conditions for 13-second grindingintervals (passes). Following each 13-second interval, the workpiece wascooled to room temperature and weighed to determine the cut of theabrasive operation. The test endpoint was determined when the cut fellbelow 15 grams per cycle. Test results were reported as the incrementalcut (g/cycle) for each interval and the total stock removed (g).

Results reported in Table 2 (below) were obtained according to theGrinding Tests.

TABLE 2 MILD STEEL CUT, grams COMPARATIVE COMPARATIVE COMPARATIVEEXAMPLE 1 EXAMPLE B EXAMPLE 2 EXAMPLE A EXAMPLE C HIGH PRESSURE GRINDINGTEST METHOD A LOW PRESSURE GRINDING TEST METHOD B CYCLE Test 1 Test 2Test 1 Test 2 Test 1 Test 2 Test 1 Test 2 Test 1 Test 2 1 23.1 20.5825.48 25.84 24.56 25.76 22.88 23.9 29.8 29.21 2 23.5 21.73 24.42 25.0329.13 30.46 23.53 24.71 36.58 34.14 3 23.73 22.71 23.8 24.24 34.6 34.4126.46 27.87 35.85 36.37 4 22.35 22.57 23.34 23.84 37.76 37.86 26.7228.99 35.03 35.22 5 22.82 22.85 22.66 23.31 39.86 38.23 26.46 29.6135.48 35.7 6 22.4 23.44 21.93 23.33 38.55 36.07 27.48 28.04 34.49 33.1 722.2 22.8 21.89 22.97 36.57 35.54 26.33 27.99 32.91 33.2 8 22.28 22.8421.45 22.9 36.91 35.47 26.99 28.2 32.63 32.71 9 22.22 22.99 21.14 22.9236.35 35.86 26.83 28.87 31.15 31.6 10 22.01 22.72 21 22.76 36.53 35.7526.4 29.3 31.13 31.49 11 21.81 22.75 20.45 22.19 35.87 36.51 25.6 29.4930.77 31.12 12 21.59 22.03 20.06 22.1 34.34 35.74 25.87 29.06 29.5130.74 13 21.56 22.49 19.82 21.87 33.85 32.65 25.34 30.04 29.71 30.37 1421.37 21.92 19.61 21.28 32.6 38.83 25.75 29.8 30.18 30.5 15 21.41 21.4919.57 20.97 32.44 37.58 25.84 28.86 29.49 30.11 16 21.04 21.24 19.5720.8 32.29 36.27 25.43 28.73 29.01 28.01 17 21 21.15 18.96 19.75 32.1836.16 25.94 28.26 29.53 28.44 18 20.78 21.14 17.93 20.04 30.99 34.3724.27 28.42 28.25 27.98 19 20.74 21.14 18.34 19.61 30.03 34.08 24.2328.84 28.42 27.75 20 20.7 20.9 18.33 19.64 31.3 31.3 24.9 29.07 28.4728.32 21 20.35 20.4 18.14 19.59 30.78 31.08 25.32 28.28 27.95 28.36 2220.4 20.43 17.97 18.95 31.71 28.44 25.29 28.56 27.95 26.51 23 20.3820.08 17.63 18.87 30.97 28.66 24.83 27.91 27.31 27.46 24 19.94 20.217.46 18.53 30.5 28.53 25.18 26.94 27.51 27.3 25 19.89 20.19 17.23 18.4129.99 27.89 24.94 27.35 26.95 26.47 26 19.6 20.08 17.64 18.27 28.9827.28 24.73 26.97 26.09 26.93 27 19.37 19.84 17.19 18.03 29.38 28.0424.58 26.6 26.02 26.33 28 19.24 19.67 16.51 17.77 29.34 27.71 24.5926.95 25.99 25.78 29 19.18 20.06 16.08 18.04 29.09 26.27 24.34 27.4326.49 26.05 30 18.79 19.7 15.44 17.54 28.53 25.9 24.03 26.61 26.44 25.7131 18.81 19.49 16.94 17.6 28.4 25.92 23.78 27.62 26.1 26.1 32 18.4319.51 15.75 17.31 28.37 26 23.99 27.12 26.34 26.18 33 18.36 19.08 15.8817.51 28.5 24.98 23.93 26.73 25.5 25.24 34 18.37 18.77 15.32 17.34 26.6427.37 23.64 26.91 25.57 25.11 35 17.89 18.98 15.55 17 26.89 26.93 23.4426.67 25.01 26.12 36 17.7 18.77 15.1 17.23 27.62 25.2 23.11 26.55 24.8825.07 37 17.71 18.49 15.21 16.88 26.95 23.76 23.58 26.15 25.25 25.12 3817.68 18.39 14.9 16.72 26.58 23.97 22.59 26.11 24.84 24.87 39 17.7118.14 14.98 16.83 26.25 24.34 22.73 26.48 25.1 24.54 40 17.74 18.0514.59 16.31 26.31 26.21 22.61 25.8 24.7 24.67 41 17.57 17.92 14.51 16.5625.92 23.94 22.29 26.44 23.92 24.45 42 16.85 17.61 14.04 16.18 26.1123.4 22.43 26.83 23.96 23.86 43 17.34 17.68 14.02 16.01 25.5 24.17 22.7226.56 24 23.81 44 17.16 17.5 13.96 16.13 25.85 22.53 22.22 26.76 23.5823.52 45 16.89 17.45 13.85 16.01 23.86 25.02 22.31 26.3 23.49 23.63 4616.74 17.58 13.86 15.71 24.59 22.93 22.15 25.94 23.19 23.06 47 16.6317.31 13.1 15.63 24.3 22.48 21.98 25.9 23.06 23.01 48 16.34 17.12 13.1315.08 23.97 23.98 21.94 25.77 22.25 22.36 49 16.28 17.05 13.14 14.8424.48 22.39 21.97 25.56 21.98 22.5 50 16.17 17.12 12.98 14.79 23.8524.31 21.73 25.4 22.33 22.71 51 16 17.04 13.14 14.55 23.86 22.16 21.6225.58 22.43 22.52 52 15.99 16.88 12.93 14.39 22.95 24.89 21.16 25.3922.31 22.42 53 15.85 16.67 12.8 14.23 23.78 22.05 21.27 25.07 22.4522.49 54 15.51 16.5 12.8 14.01 23.3 21.9 21.07 25.02 21.76 21.78 5515.37 16.21 12.84 13.98 23.6 21.18 20.98 25.12 22.31 21.79 56 14.9816.16 12.42 14.06 22.79 22.02 21.13 25.17 21.72 21.69 57 14.89 16.1412.54 13.69 22.15 20.3 20.87 24.99 21.33 21.87 58 14.7 15.99 12.23 13.8922.06 20.26 20.97 25.5 21.24 21.78 59 14.52 15.1 12.05 13.4 21.89 19.6920.54 25.34 20.94 21.6 60 14.49 15.82 12.08 13.4 22.19 21.52 20.33 24.6120.97 21.39 61 14.15 15.96 11.68 12.96 22.01 19.86 20.35 24.33 20.721.68 62 14.37 15.78 12.99 21.73 19.64 20.28 24.15 21.16 21.91 63 14.1315.38 12.87 21.58 20.38 20.08 23.99 20.57 21.61 64 13.95 15.32 12.8620.74 21.18 20.08 24.2 20.72 21.53 65 13.72 15.4 12.87 21.12 18.9 20.2923.76 20.14 21.32 66 13.66 15.06 12.71 20.45 21.44 19.97 23.89 19.8621.08 67 13.46 15.11 12.44 20.39 18.84 19.88 23.75 20.79 21.12 68 13.2615.16 12.36 20.63 17.96 20.01 23.38 19.41 20.45 69 12.96 14.98 12.2719.83 18.02 19.65 23.1 19.14 20.98 70 13.07 15.01 12.09 19.74 19.7419.21 22.8 19.66 20.76 71 12.67 14.76 11.91 19.87 19.07 19.34 22.4219.54 20.32 72 12.58 14.63 18.97 20.26 19.58 22.56 18.89 20.67 73 12.3814.6 19.27 17.93 18.78 22.45 19.19 20.21 74 12.24 14.54 18.64 18.0518.67 22.12 19.09 20.25 75 12.33 14.36 18.4 16.6 18.31 22.29 18.66 19.9976 12.11 14.36 18.31 18.37 18.28 21.61 18.36 19.93 77 11.92 14.32 18.1116.47 18.47 21.84 18.51 20.12. 78 14.05 17.64 17.21 18.5 21.29 18.2819.92 79 14 17.56 16.91 18.15 21.48 18.21 19.92 80 13.71 17.35 16.1918.46 21.59 18.02 19.93 81 13.68 16.98 16.4 17.93 21.15 17.43 19.87 8213.44 16.98 16.74 18.5 21.09 17.72 19.87 83 13.33 16.85 15.96 18.2320.79 17.63 19.94 84 13.26 16.4 16.9 18.1 21.09 17.83 19.9 85 13.26 16.216.76 18.52 21.07 17.46 19.53 86 12.96 16.27 15.56 18.12 20.85 17.4319.65 87 13.01 15.66 16.12 18.22 21.17 17.1 19.48 88 12.84 15.4 15.618.04 20.73 16.86 19.32 89 12.75 15.32 15.02 17.67 20.68 16.84 19.4 9012.57 15.08 15.47 17.94 20.75 16.65 19.26 91 12.46 14.96 14.59 17.9820.3 16.36 19.41 92 12.35 17.71 20.4 16.48 19.15 93 12.24 17.62 20.4316.49 19.34 94 12.07 17.89 20 16.34 19.11 95 11.85 17.97 19.91 16.4219.46 96 17.88 19.65 16.19 19.4 97 17.64 19.57 15.84 19.45 98 17.6219.16 15.89 19 99 17.47 18.76 15.62 18.51 100 17.09 18.94 15.34 19.58101 17.04 18.67 15.14 17.56 102 16.93 17.77 14.79 18.51 103 16.62 17.6118.07 104 16.15 17.5 18.1 105 16.12 16.93 17.71 106 15.77 16.78 17.28107 15.63 16.71 17.39 108 15.48 16.71 16.8 109 15.14 16.39 16.52 11015.08 16.37 16.48 111 14.92 16.49 16.46 112 16.26 16.17 113 16.03 15.98114 14.79 15.82 115 15.68 15.32 116 15.74 15.01 117 15.58 14.91 11815.22 119 14.84 TOTAL 1359 1655 1019 1235 2294 2233 2346 2797 2352 2685CUT

All cited references, patents, and patent applications in the aboveapplication for letters patent are herein incorporated by reference intheir entirety in a consistent manner. In the event of inconsistenciesor contradictions between portions of the incorporated references andthis application, the information in the preceding description shallcontrol. The preceding description, given in order to enable one ofordinary skill in the art to practice the claimed disclosure, is not tobe construed as limiting the scope of the disclosure, which is definedby the claims and all equivalents thereto.

1. A coated abrasive disc comprising: a disc backing having an outercircumference; an abrasive layer disposed on the disc backing, whereinthe abrasive layer comprises triangular abrasive platelets secured to amajor surface of the disc backing by at least one binder material,wherein the triangular abrasive platelets are disposed at least 70percent of regularly-spaced points along an arithmetic spiral patternextending outwardly toward the outer circumference, wherein each one ofthe triangular abrasive platelets has respective top and bottom surfacesconnected to each other, and separated by, three sidewalls, and wherein,on a respective basis, one sidewall of at least 90 percent of each ofthe triangular abrasive platelets disposed facing and proximate to thedisc backing, and is lengthwise aligned within 10 degrees of beingtangent to the arithmetic spiral pattern.
 2. The coated abrasive disc ofclaim 1, wherein the triangular abrasive platelets have an averagethickness, and wherein the arithmetic spiral pattern has a pitch that is1.2 to 3 times the average thickness of the triangular abrasiveplatelets.
 3. The coated abrasive disc of claim 1, wherein the abrasivelayer further comprises crushed abrasive or non-abrasive particles. 4.The coated abrasive disc of claim 1, wherein the disc backing comprisesvulcanized fiber.
 5. The coated abrasive disc of claim 1, wherein theabrasive layer comprises a make layer and a size layer disposed over themake layer and the triangular abrasive platelets.
 6. The coated abrasivedisc of claim 1, wherein the triangular abrasive platelets comprisealpha alumina.
 7. A method of abrading, the method comprisingfrictionally contacting a portion of the abrasive layer of a coatedabrasive disc according to claim 1 with a substrate, and moving at leastone of the substrate and the coated abrasive disc relative to the otherto abrade the substrate.
 8. The method of claim 7, wherein the substratecomprises a mild steel weld, and wherein the abrasive layer contacts themild steel weld.
 9. A method of making a coated abrasive disc, themethod comprising: disposing a curable make layer precursor on a majorsurface of a disc backing having an outer circumference; adheringtriangular abrasive platelets into the curable make layer precursor,wherein the triangular abrasive platelets are disposed at least 70percent of regularly-spaced points along an arithmetic spiral patternextending outwardly toward the outer circumference, wherein thetriangular abrasive platelets comprise triangular abrasive platelets,wherein each one of the triangular abrasive platelets has respective topand bottom surfaces connected to each other, and separated, by threesidewalls, and wherein, on a respective basis, one sidewall of at least90 percent of each of the triangular abrasive platelets is entirelydisposed proximate the disc backing, and is lengthwise aligned within 10degrees of being tangent to the arithmetic spiral pattern; at leastpartially curing the curable make layer precursor to provide a makelayer; disposing a curable size layer precursor over the make layer andtriangular abrasive platelets; and at least partially curing the curablesize layer precursor to provide a size layer.
 10. The method of claim 9,wherein the triangular abrasive platelets have an average thickness, andwherein the arithmetic spiral pattern has a pitch that is 1.2 to 3 timesthe average thickness of the triangular abrasive platelets.
 11. Themethod of claim 9, wherein the abrasive layer further comprises crushedabrasive or non-abrasive particles.
 12. The method of claim 9, whereinthe disc backing comprises vulcanized fiber.
 13. The method of claim 9,wherein the triangular abrasive platelets comprise alpha alumina.